Stephanie Innes | Alison Steinbach | Arizona Republic

The highly contagious delta variant appears to be the dominant strain of the COVID-19 virus in Arizona, mirroring what’s happening nationwide.

“We are finding delta pretty much everywhere now,” said David Engelthaler, director of the infectious disease branch of the Arizona-based Translational Genomics Research Institute. “It is officially our dominant strain and likely will remain that way until and unless another variant shows up that can spread even faster than delta.”

What that means for Arizonans who aren’t vaccinated or don’t have immunity to COVID-19 is that they are at higher risk of contracting the virus that causes it. That’s because the delta variant spreads so much more efficiently than other strains of the virus.

Arizona on Monday ranked seventh-highest among U.S. states and territories for its seven-day rate of new COVID-19 cases, behind Missouri, Arkansas, Florida, Louisiana, the Virgin Islands and Nevada, according to the U.S Centers for Disease Control and Prevention.

Over the past three weeks, the delta variant, which was first detected in India and is also known as B.1.617.2, has risen in proportion from about 30% to about 50% of all sequenced COVID-19 cases in Arizona, Engelthaler said. In the U.S., delta is the dominant variant of COVID-19, CDC data shows.

“If we look more closely within our data we can see that within the last three weeks, it’s looking like it’s probably between 50% and 60%, which matches up with where the CDC is forecasting as well for current sequencing around the country,” Engelthaler said. “That’s really giving us a view on how the virus has evolved and what is most successfully being transmitted.”

Less than half of Arizonans are fully vaccinated, data shows

About 49% of the total U.S. population was fully vaccinated as of Monday, meaning two weeks out from their final shot, according to the CDC. In Arizona, the CDC data shows 44.5% of the total population was fully vaccinated as of Monday, and 52% of the Arizona population had received at least one dose.

The delta variant of the SARS-CoV-2 virus that causes COVID-19 has been detected across Arizona, but primarily in Maricopa, Pinal and Pima counties where most people live, and where most COVID-19 cases are occurring, Engelthaler said.

The CDC and labs in Arizona that do genome sequencing of positive COVID-19 samples have also identified cases of the delta variant in Yuma, Cochise, Coconino, Mohave and Navajo counties, according to officials with TGen, which maintains a COVID-19 variant dashboard.

“At any given time, about 10% to 13% of the cases are sequenced, so we get a really good view. And we do get sequenced data from around the state,” Engelthaler said. “I would anticipate there’s a couple of thousand, maybe several thousand cases of delta total in Arizona.”

The rapid transmission of the delta variant has created what CDC director Dr. Rochelle Walensky recently called “a pandemic of the unvaccinated.”

“It’s very clear that the serious cases, the ones that become hospitalized, or worse, death — those are the ones that are unvaccinated,” Engelthaler said.

“Over 99% of hospitalized cases are people who were not vaccinated, so that is why the CDC director made that remark. I think it’s an apt remark and it just means that the concern is not among the people that are vaccinated.”

During a U.S. Senate Committee on Health, Education, Labor and Pensions hearing on Tuesday, Walensky said the delta variant’s prevalence in the U.S. has soared to represent about 83% of sequenced cases.

“This is a dramatic increase, up from 50% the week of July 3rd. In some parts of the country, the percentage is even higher, particularly in areas of low vaccination rates,” she said.

“Each death is tragic and even more heartbreaking when we know that the majority of these deaths could be prevented with a simple, safe, available vaccine.”

State: Most new COVID-19 cases in AZ are in unvaccinated people

About 95% of Arizona’s COVID-19 cases in May and 92% of the reported cases in June were among people not fully vaccinated, according to the state health department. About 99% of COVID-19 deaths in Arizona in 2021 were among people not fully vaccinated.

Hospitals in Arizona are reporting increases in COVID-19 patient numbers, and case numbers are up, too. The concern right now is for people who don’t have immunity, either because they did not get vaccinated, or they didn’t have a prior infection.

“Everywhere it shows up, it becomes the dominant strain,” Engelthaler said of the delta variant. “It just out-competes the other strains.”

Some so-called “breakthrough” cases of COVID-19 are occurring in people who are fully vaccinated, but they are rare. Federal, state and county health officials say the COVID-19 vaccine is the best way prevent transmission of the delta variant, which is causing waves of hospitalizations in pockets of the country where vaccination rates are low.

State health officials last week said Arizona had recorded more than 3,500 breakthrough cases out of more than 3.2 million fully vaccinated people. Twenty-eight of them had died.

There is some debate about whether the delta variant is making people sicker. Engelthaler said from the evidence he’s seen, delta does not appear to be causing more severe illness than any other COVID-19 strain.

“It’s just more effective at finding the next susceptible person That’s why we are seeing case numbers increasing. They are not skyrocketing but they are increasing and that’s because this is the most efficient strain of this virus out there and it’s like water. It finds the cracks,” Engelthaler said.

In an interview posted on the Harvard T.H. Chan School of Public Health’s website, Harvard associate professor of epidemiology William Hanage is quoted as saying the delta variant is about 60% more transmissible than the previously dominant alpha variant, which originated in the United Kingdom and is also known as B.1.1.7. He also said it appears to have higher viral loads earlier in infection.

Those higher viral loads “may mean that it’s even more infectious during the period when people don’t yet realize they’re infected,” Hanage is quoted as saying. “Delta’s greater virulence means that unvaccinated people who become infected will be sicker and the burden on the health care system will be greater.”

Without more immunity in the population, delta could mutate into a deadlier variant

The past week has seen daily new case reports mostly of more than 1,000, according to the state, a level Arizona has not seen since March.

The state’s seven-day average for new cases, 1,219 as of Tuesday, was the highest since mid-March, and more than double the average from two weeks ago, which was 543. The seven-day average had reached as high as 9,800 in January, according to state data.

“If you don’t have immunity either from vaccination or previous infection, you are still at risk. In fact you are at higher risk now for getting infected because this variant is such an efficient spreader,” Engelthaler said.

Officials with the Arizona Department of Health Services did not immediately respond to a question about where in the state the delta variant is most commonly found. The department last month said it was aware of at least four potential outbreaks of COVID-19 involving 10 or more people that have occurred since May, but did not confirm whether those possible outbreaks involved the delta variant.

An outbreak tied to a country-western dance near Show Low in Navajo County has been linked to 24 positive COVID-19 cases, including two deaths. While many of those who attended the dance believe the delta variant is to blame, state and county health officials say they cannot confirm whether that is true.

Fewer than 40% of the population in the ZIP code that includes Show Low and the area where the dance hall is located have received at least one dose of the COVID-19 vaccine, state data shows. And at the area’s hospital — Summit Healthcare Regional Medical Center — only about 30% of the staff has been vaccinated, officials at the hospital recently told The Arizona Republic.

The problem with continued transmission of the COVID-19 virus is that it continues to replicate, creating a higher risk that it could mutate into a more deadly or vaccine-resistant variant.

And COVID-19 is a global problem, Engelthaler emphasized. Stopping the variants from circulating won’t happen through the efforts of one country alone, he said.

“(The U.S. is) doing great compared to most of the rest of the world. In many countries in Africa we’re seeing less than 5% immunization rates,” Engelthaler said. “That means there’s a lot of opportunity for additional mutations to occur and potentially new variants to pop up that we might have to deal with.”